Development of siRNA payloads to target KRAS-mutant cancer.

UNLABELLED: RNAi is a powerful tool for target identification and can lead to novel therapies for pharmacologically intractable targets such as KRAS. RNAi therapy must combine potent siRNA payloads with reliable in vivo delivery for efficient target inhibition. We used a functional "Sensor" assay to establish a library of potent siRNAs against RAS pathway genes and to show that they efficiently suppress their targets at low dose. This reduces off-target effects and enables combination gene knockdown. We administered Sensor siRNAs in vitro and in vivo and validated the delivery of KRAS siRNA alone and siRNA targeting the complete RAF effector node (A/B/CRAF) as promising strategies to treat KRAS-mutant colorectal cancer. We further demonstrate that improved therapeutic efficacy is achieved by formulating siRNA payloads that combine both single-gene siRNA and node-targeted siRNAs (KRAS + PIK3CA/B). The customizable nature of Sensor siRNA payloads offers a universal platform for the combination target identification and development of RNAi therapeutics. SIGNIFICANCE: To advance RNAi therapy for KRAS-mutant cancer, we developed a validated siRNA library against RAS pathway genes that enables combination gene silencing. Using an in vivo model for real-time siRNA delivery tracking, we show that siRNA-mediated inhibition of KRAS as well as RAF or PI3K combinations can impair KRAS-mutant colorectal cancer in xenograft models. ©2014 American Association for Cancer Research.